Obviously, this could be a harware failure, but I have had a few similar events on an otherwise stable setup. My solution has been to separate the connection, close ProntoEdit, and power cycle the Pronto. On rare occasions I needed to reboot the computer. I program quite a few Pronto's and this little glitch will bite once or twice a year. It is annoying, but not a big deal for me.

I can't take away your observation that pressing helped. I recommend not pressing your luck (sorry) because if a little pressing gave positive results, more pressing will be used the next time and eventually something will break, and tend to confirm your suspecion.